1. Field of the Invention
This invention relates generally to implantable devices for interventional therapeutic treatment or vascular surgery, and more particularly concerns an occlusion coil assembly with defined segments attached together by connector members that can be activated to release desired selected segments of the coil assembly.
2. Description of Related Art
Interventional vascular therapy and surgery has recently involved the use of catheters to place therapeutic devices at a treatment site by access through the vasculature. Examples of such procedures include transluminal angioplasty, placement of stents to reinforce the walls of a blood vessel or the like and the use of vasoocclusive devices to treat defects in the vasculature. One specific field of interventional therapy that has been able to advantageously use recent developments in technology is the treatment of neurovascular defects. One type of non-surgical therapy that has become advantageous for the treatment of defects in the neurovasculature has been the placement of vasoocclusive devices by way of a catheter in a damaged portion of a vein or artery.
Vasoocclusion devices are therapeutic devices that are placed within the vasculature of the human body, typically via a catheter, either to block the flow of blood through a vessel making up that portion of the vasculature through the formation of an embolus or to form such an embolus within an aneurysm stemming from the vessel. The vasoocclusive devices can take a variety of configurations, and are generally formed of one or more elements that are larger in the deployed configuration than when they are within the delivery catheter prior to placement. One widely used vasoocclusive device is a helical wire coil having a deployed configuration which may be dimensioned to engage the walls of the vessels. One anatomically shaped vasoocclusive device that forms itself into a shape of an anatomical cavity such as an aneurysm and is made of a pre-formed strand of flexible material that can be a nickel-titanium alloy is known from U.S. Pat. No. 5,645,558, which is specifically incorporated by reference herein. That vasoocclusive device comprises one or more vasoocclusive members wound to form a generally spherical or ovoid shape in a relaxed state. The device is sized and shaped to fit within a vascular cavity or vesicle, such as for treatment of an aneurysm or fistula. The vasoocclusive member can be first helically wound or braided in a generally linear fashion, and is then wound around an appropriately shaped mandrel or form, and heat treated to retain the shape after removal from the heating form. Radiopacity can be provided in the vasoocclusive members by weaving in synthetic or natural fibers filled with powdered radiopaque material, such as powdered tantalum, powdered tungsten, powdered bismuth oxide or powdered barium sulfate, which can potentially be released during vascular surgery.
The delivery of such vasoocclusive devices can be accomplished by a variety of means, including via a catheter in which the device is pushed through the catheter by a pusher to deploy the device. The vasoocclusive devices, which can have a primary shape of a coil of wire that is then formed into a more complex secondary shape, can be produced in such a way that they will pass through the lumen of a catheter in a linear shape and take on a complex shape as originally formed after being deployed into the area of interest, such as an aneurysm. A variety of detachment mechanisms to release the device from a pusher have been developed and are known in the art.
For treatment of areas of the small diameter vasculature such as a small artery or vein in the brain, for example, and for treatment of aneurysms and the like, micro-coils formed of very small diameter wire are used in order to restrict, reinforce, or to occlude such small diameter areas of the vasculature. A variety of materials have been suggested for use in such micro-coils, including nickel-titanium alloys, copper, stainless steel, platinum, tungsten, various plastics or the like, each of which offers certain benefits in various applications. Nickel-titanium alloys are particularly advantageous for the fabrication of such micro coils, in that they can have super-elastic or shape memory properties, and thus can be manufactured to easily fit into a linear portion of a catheter, but attain their originally formed, more complex shape when deployed.
In some applications, it has been found that the correct length of such microcoil occlusive devices for use at a treatment site in the vasculature is only determined after delivery of the device. Thus, typically a physician will choose a standard length, such as a 20 cm coil, for example, without knowing that only a 15 or 16 cm coil is the proper length. When it is discovered that a shorter coil is required, the entire coil needs to be removed and replaced with a shorter coil taking time to withdraw and replace with the proper length. In addition, if it is discovered that a longer coil is required, another procedure must be performed to supply the additional coil length. In either case, the entire treatment procedure is prolonged, resulting in potential trauma to the patient.
A need therefore remains for a microcoil occlusive device that will allow the precise required length of coil to be supplied to a desired treatment site in a minimally traumatic procedure. It would be desirable to provide a device that allows a physician to introduce a coil of ample length for any given treatment site in the vasculature, detach one or more desired coil lengths at the treatment site, and reposition the catheter and continue to deploy the remaining coil segments as desired, in a single procedure. The present invention meets these and other needs.
Briefly, and in general terms, the present invention provides for an occlusion coil assembly composed of detachable segments that can be detached and placed as desired at one or more vascular treatment sites, for use in interventional therapy and vascular surgery.
The invention accordingly provides for an occlusion coil assembly for use in interventional therapy and vascular surgery, adapted to be inserted into a portion of a vasculature of a patient. The occlusion coil assembly includes a plurality of hollow, tubular coil segments, and a plurality of connector members, with adjacent coil segments connected together by the connector members. The connector members are currently preferably hollow, tubular connector members that are advantageously detachable from selected portions of the coil segments by application of energy to one or more selected connector members. In a currently preferred embodiment, the connector members are formed of a shape memory material, preferably having a glass transition temperature (Tg) above body temperature, and having a desired stressed configuration at a temperature appropriate for introduction into the body via a catheter, and a more relaxed, unstressed original shape that is assumed upon activation for releasing the endoluminal therapeutic device. The shape memory material is currently preferably a shape memory polymer, such as polyurethane, heat shrink tubing such as polyethylene terephthalate (PET) or high density polyethylene (HDPE), although the shape memory material may alternatively be a shape memory metal such as nickel titanium alloy, such as that available under the trade name NITINOL, for example, that can be heat treated to have shape memory behavior.
The shape memory material sections are currently preferably secured to the coil segments by crimping a distal portion of a shape memory material connector member over a proximal portion of a segment of the coil assembly, and securing, such as by gluing, a proximal portion of the shape memory material connector member over a distal portion of a segment of the coil assembly. Alternatively, the shape memory material connector members can be secured to the coil segments such as by gluing a distal portion of a shape memory material connector member over a proximal portion of a coil segment, and crimping a proximal portion of the shape memory material connector member over a distal portion of a coil segment. As the sections are detached by heat activation, the activated shape memory material connector member radially opens and axially shrinks, separating one or more distal coil segments from the proximal portion of the coil assembly.
In operation of the occlusion coil assembly, a heat activation member is also preferably provided for heating one or more selected connector members to disconnect selected portions of the coil assembly. The heat activation member typically can be advanced and retracted axially through the middle of the coil assembly, or by means of a catheter that has a light source at the distal tip, for example, and currently preferably comprises a fiber optic, although the heat activation member can also comprise a heat pipe, or a device for generating heat by RF energy, or by electrical resistance, and the like.
From the above, it can be seen that the present invention provides an improved coil assembly that is more easily adapted to placement of coils without the risk of using an inappropriate length and the subsequent withdrawal and replacement of the coil by the therapist. These and other aspects and advantages of the invention will become apparent from the following detailed description and the accompanying drawings, which illustrate by way of example the features of the invention.